I did this activity long ago with my first toddler class, lugging my own griddle into school, but had forgotten all about it until I saw in on Pinterest. I knew I had to try it with Tyler!
We simply set our griddle on warm (not enough to really burn unless you lay your hand on it for a few seconds...supervision required!), measured some paper to fully cover the griddle (my husband reminded me of what a pain it was to removed crayon from this years ago), and grabbed our crayons.
After experimenting with his first pictures, we noticed that Ty's fat toddler crayons worked the best versus the regular sized ones. It was also easy to see that black, his favorite color, melted exceptionally well for some reason which he adored.
This was a huge hit with Tyler! I'm sure we'll be doing it again soon!
We hung his art in the windows, which made them look even more interesting and bright as we used thin paper. Tyler was most excited that he could see the white crayon this way! He often tells me that you can't see "white on white" (though he always tries anyhow), but we could here!